Method for transmitting layer 2 packet and access device thereof

ABSTRACT

A method for Layer 2 packet transmission is disclosed, where a corresponding relationship between packet attribute information and public MAC addresses is configured in an access device such that the access device could find a corresponding public MAC address in the corresponding relationship when receiving a packet from a user terminal, replaces the source MAC address with the public MAC address found, and then sends the packet to a convergence layer device. A method for transmission of a Layer 2 packet without character information is also disclosed. The access device needs to obtain the packet attribute information and carry the information in the packet to be sent to the convergence layer device. An access device is also disclosed. As a result, the capacity of the VLAN and the MAC address table items needed for the convergence layer device to convert MAC addresses is greatly decreased.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a continuation application of a U.S. applicationSer. No. 11/596,491, filed Jan. 17, 2007, entitled “METHOD FORTRANSMITTING LAYER 2 PACKET AND ACCESS DEVICE THEREOF,” by Haijun W U,which itself claims the priority of an international application No.PCT/CN2006/001011, filed May 17, 2006, entitled “A TRANSMISSION METHODFOR MASSAGE IN LAYER 2 AND AN ACCESS DEVICE THEREOF”, by Haijun W U,which itself claims the priority of a Chinese application No.200510070611.4, filed May 17, 2005, entitled “METHOD AND DEVICE OFCONVERGING LAYER 2 MAC ADDRESS”, by Haijun W U, the disclosures forwhich are hereby incorporated herein in their entireties by reference.

FIELD OF THE INVENTION

The invention relates generally to the network communication technology,and more particularly, to a method and an access device for transmittinga Layer 2 packet between an access device and a convergence layerdevice.

BACKGROUND OF THE INVENTION

At present, an Ethernet interface is used as an uplink interface in mostbroadband access networks and most convergence networks are the networksconstructed based on Layer 2 or Layer 3 switches. As shown in FIG. 1,upon accessed by a user, the broadband access device gets connected witha centralized broadband access server (BRAS) or routing device throughthe convergence network. Usually, an Ethernet switch or a convergencedevice may be connected to several to dozens of broadband access devicesand each broadband access device may be connected to as many as hundredsof user terminals. Therefore, the number of the users accessing theLayer 2 convergence network may be up to tens of thousands. However, theEthernet switch performs the switch function based on a media accesscontrol (MAC) address and a virtual local area network (VLAN), and theEthernet switches with MAC based forwarding table of 4 k, 8 k, 32 k and64 k are used usually at present. Therefore, the switching table itemsthat an Ethernet switch can accommodate are limited.

With the development of multiple services, a family accessing thenetwork with broadband may have a plurality of service terminals andeach terminal has a Layer 2 MAC address. As a result, the capacity ofthe VLAN and MAC address table items currently supported by theconvergence network are unable to satisfy the demand of the servicedevelopment.

To enable the convergence layer device to satisfy the demand of theservice development, a method for performing Layer 3 routing in abroadband access device, such as a digital subscriber line accessmultiplexer (DSLAM), may be adopted. That is, upon receiving a Layer 2packet from a user terminal, the broadband access device replaces asource Layer 2 MAC address in the packet with a Layer 3 interface MACaddress thereof. In this way, the packet transmitted upward from thebroadband access device only carries a Layer 3 interface MAC address ofthe broadband access device, thereby the demand for the MAC addressforwarding table items associated with the convergence device in thenetwork is dramatically decreased. However, upon performing the Layer 3protocol, the broadband access device has to assign an IP address forthe user thereon. As there are a great number of broadband accessdevices in the network, the IP address space will be very scattered ifeach broadband access device is assigned with an IP address segment toachieve the above objective, and this greatly decreases the utilizingratio of address and goes against the maintenance of the network.

Therefore, a heretofore unaddressed need exists in the art to addressthe aforementioned deficiencies and inadequacies.

SUMMARY OF THE INVENTION

The present invention provides a method and an access device fortransmitting a Layer 2 packet.

In one embodiment, the method for transmitting a Layer 2 packet includessetting up corresponding relationship between packet attributeinformation and a public media access control (MAC) address andconfiguring the corresponding relationship in an access device, and theaccess device receiving a packet from a user terminal, finding thecorresponding public MAC address from the corresponding relationshipaccording to the attribute information of the packet, replacing a sourceMAC address in the packet with the public MAC address, and sending thepacket to a convergence layer device.

The attribute information of the packet includes at least one of thetype of a protocol adopted by the packet, the type of a link bearing thepacket and the type of a user group to which the user terminal sendingthe packet belongs.

The method further includes: after the access device finds thecorresponding public MAC address, the access device obtaining thecharacter information of the packet and setting up an index relationshipbetween the character information of the packet and the source MACaddress of the packet.

The character information of the packet includes at least one of asource internet protocol (IP) address, a session identifier (ID) and adestination IP address of the packet.

The method further includes the access device receiving a packet fromthe convergence layer device, extracting the packet characterinformation from the packet, finding the corresponding source MACaddress from the index relationship according to the characterinformation of the packet, and sending the packet to the user terminal.

A method for transmitting a Layer 2 packet carrying no characterinformation, includes setting up corresponding relationship betweenpacket attribute information and a public MAC address and configuringthe corresponding relationship in an access device, and the accessdevice receiving a packet carrying no character information from a userterminal, finding the corresponding public MAC address from thecorresponding relationship according to the attribute information of thepacket, replacing a source MAC address with the public MAC address,obtaining the character information of the packet, making the characterinformation carried in the packet and sending the packet to aconvergence layer device, and meanwhile, setting up an indexrelationship between the character information of the packet and thesource MAC address of the packet.

The character information of the packet is user port informationcorresponding to the packet.

The user port information includes at least one of frame information,slot information and a port number of the access device receiving thepacket, and the source MAC address of the packet.

The packet carrying no character information includes the first packetsupporting a point-to-point protocol over Ethernet (PPPOE) or a DynamicHost Configuration Protocol (DHCP) from the user terminal.

The character information of the packet is carried in an Immediate RelayAgent field when the packet carrying no character information is thefirst packet supporting the point-to-point protocol over Ethernet(PPPOE) from the user terminal.

The method further includes upon receiving the packet from the accessdevice, the convergence layer device storing the character informationcarried in the packet and setting the character information in adownstream packet before sending the downstream packet to the accessdevice, and upon receiving the downstream packet, the access deviceextracting the character information from the packet, finding the sourceMAC address corresponding to the extracted character informationaccording to the self-stored index relationship between the characterinformation of the packet and the source MAC address, replacing thedestination MAC address with the source MAC address and sending thepacket to the corresponding user terminal.

In another aspect, this invention provides an access device, includingan MAC address conversion module, for receiving an upstream packet froma user terminal, finding a public MAC address corresponding to thepacket according to self-stored corresponding relationship betweenpacket attribute information and the public MAC address, replacing asource MAC address of the upstream packet with the public MAC addressand then sending the packet to a convergence layer device.

The MAC address conversion module is located in a hardware processingunit of the access device.

The access device further includes a user terminal MAC addressdetermining module, for receiving a downstream packet from theconvergence layer device, carrying character information of the packetin a user terminal MAC address request and sending the request to theuser terminal MAC address conversion module, replacing a destination MACaddress of the downstream packet with the user terminal MAC addressreturned by the user terminal MAC address conversion module and sendingthe packet to the corresponding user terminal, wherein the user terminalMAC address conversion module is further for use in storing an indexrelationship between the packet character information and the source MACaddress, finding the corresponding source MAC address in the indexrelationship upon receiving the user terminal MAC address requestcarrying the packet character information, and sending the source MACaddress as the user terminal MAC address to the user terminal MACaddress determining module.

The user terminal MAC address determining module is located in thehardware processing unit of the access device.

The access device further includes an application layer MAC addressconversion module located in a software processing unit of the accessdevice, for obtaining the public MAC address of the packet from the MACaddress conversion module upon receiving the application layerassociated upstream packet from the hardware processing unit of theaccess device, replacing the source MAC address of the packet with theobtained public MAC address and sending the packet to a forwardingmodule in the hardware processing unit of the access device.

The access device further includes an application layer user terminalMAC address determining module located in the software processing unitof the access device, for receiving the application layer associateddownstream packet sent from the hardware processing unit of the accessdevice, requesting the corresponding user terminal MAC address from theapplication layer MAC address conversion module according to thecharacter information of the packet, replacing the destination MACaddress of the downstream packet with the user terminal public MACaddress returned from the application layer MAC address conversionmodule and sending the packet to the forwarding module in the hardwareprocessing unit of the access device, wherein the application layer MACaddress conversion module is further for use in storing the indexrelationship between the packet character information and the source MACaddress, and according to the request from the application layer userterminal MAC address determining module, returning the source MACaddress corresponding to the packet character information sent from theapplication layer user terminal MAC address determining module as theapplication layer user terminal MAC address to the user terminal MACaddress determining module.

The application layer MAC address conversion module further includes auser port information obtaining module, for receiving the upstreampacket sent by the hardware processing unit and detecting the packet; ifthe packet contains no character information, acquiring the user portinformation of the packet from the hardware processing unit andregarding the acquired user port information as the characterinformation of the packet.

In comparison with the prior art, according to this invention, acorresponding relationship between packet attribute information andpublic MAC address is set up and is configured on the access device.When receiving a packet from a user terminal, the access device findsthe corresponding public MAC address from the corresponding relationshipaccording to the attribute information of the packet, replaces thesource MAC address with the public MAC address, and then sends thepacket to the convergence layer device. As a result, the capacity of theVLAN and the MAC address table items needed for the convergence layerdevice to convert MAC addresses is dramatically decreased. Meanwhile, itis unnecessary for the access device to assign IP addresses for users,thereby facilitating the maintenance of the network.

These and other aspects of the present invention will become apparentfrom the following description of the preferred embodiment taken inconjunction with the following drawings, although variations andmodifications therein may be affected without departing from the spiritand scope of the novel concepts of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate one or more embodiments of theinvention and, together with the written description, serve to explainthe principles of the invention. Wherever possible, the same referencenumbers are used throughout the drawings to refer to the same or likeelements of an embodiment, and wherein:

FIG. 1 is a schematic diagram illustrating the networking of theEthernet;

FIG. 2 is a flowchart for uplink transmission of a Layer 2 packetaccording to an embodiment of the invention;

FIG. 3 is a flowchart for downlink transmission of a Layer 2 packetaccording to an embodiment of the invention;

FIG. 4 is the first schematic diagram illustrating the structure of anaccess device for transmitting a Layer 2 packet according to anembodiment of the invention;

FIG. 5 is the second schematic diagram illustrating the structure of anaccess device for transmitting a Layer 2 packet according to anembodiment of the invention; and

FIG. 6 is the third schematic diagram illustrating the structure of anaccess device for transmitting a Layer 2 packet according to anembodiment of the invention.

EMBODIMENTS OF THE INVENTION

In the present invention, according to the attribute of the packets, anaccess device replaces the source MAC addresses of the packets havingthe same attribute with one public MAC address, and then sends thepackets to a convergence device.

The invention will be further described in detail with reference to theaccompanying drawings and preferred embodiments.

The transmission of Layer 2 packet mentioned above specifically includesthe transmission of an upstream packet and the transmission of adownstream packet, which will be described hereinafter, respectively.

FIG. 2 is a flowchart for uplink transmission of a Layer 2 packetaccording to an embodiment of the invention. As shown in FIG. 2, thespecific steps are described as follows:

Step 201: Pre-configure a corresponding relationship between packetattribute information and public MAC address in an access device.

The packet attribute information may be the type of the protocol adoptedby the packet, or the type of the link bearing the packet, such as thetype of the permanent virtual channel (PVC) of the user terminal port,or the type of the user group to which the user terminal sending thepacket belongs.

Step 202: The access device receives an Ethernet packet from a userterminal.

The Ethernet packet sent from the user terminal to the access device maybe an IP over Ethernet (IPoE) packet, or a point-to-point protocol overEthernet (PPPOE) packet, etc.

Step 203: The access device finds the public MAC address correspondingto the Ethernet packet from the corresponding relationship betweenpacket attribute information and public MAC address according to theattribute information of the Ethernet packet, wherein the correspondingrelationship between the packet attribute information and the public MACaddress is configured in the access device.

For example, when the packet attribute information is the type of thepermanent virtual channel (PVC) of the user terminal port, the MACaddress 1 may be used as the public MAC address if the packet comes fromthe PVC 1 of the user terminal port. Similarly, the MAC address 2 may beused as the public MAC address if the packet comes from the PVC2 of theuser terminal port, and so on, wherein the user terminal is the terminalsending a packet.

Step 204: The access device obtains the character information of thepacket.

The character information of the packet in this step must be thecharacter information of uniqueness distinguishing the packet fromothers.

The character information may be obtained from the packet when thepacket includes the unique character information therein. In this case,the character information of the packet may be a source internetprotocol (IP) address, a session identifier (ID), or a destination IPaddress. For example, the source IP address of the packet may beextracted as the character information when the packet is an IPoE packetor an Address Resolution Protocol (ARP) request packet. The PPPoEsession identifier or the source IP address may be extracted as thecharacter information when the packet is a PPPoE packet. The destinationIP address packet may be extracted as the character information when thepacket is an ARP response packet.

The user port information corresponding to the packet may be used as thecharacter information of the packet when the packet does not include thecharacter information therein, e.g., the character information is notincluded in the first PPPoE packet or in the first Dynamic HostConfiguration Protocol (DHCP) packet sent from a user terminal. The userport information may include the frame information, slot information andport number of the access device receiving the packet, or the user portinformation may be the source MAC address of the packet, or the userport information may include the frame information, slot information andport number of the access device receiving the packet as well as thesource MAC address of the packet. The access device needs to add theuser port information corresponding to the packet to the upstreampacket, and then, the convergence device adds the user port informationto the downstream packet when sending the downstream packet. Forexample, for the PPPoE uplink packet and downstream packet, the userport information may be added to an Immediate Relay Agent field suchthat the access device could find the user terminal MAC addresscorresponding to the destination MAC address of the downstream packetaccording to the user port information.

Step 205: The access device sets up an index relationship between thecharacter information of the packet and the source MAC address of thepacket.

The index relationship is used for converting the Layer 2 MAC address ofthe downstream packet.

Step 206: The access device replaces the source MAC address of theEthernet packet with the found public MAC address, and then sends thepacket to the convergence layer device.

It can be seen that the MAC address forwarding table items needing to besetup by the convergence layer device are greatly decreased because theaccess device replaces the source MAC addresses of the packets havingthe same attribute from the user terminal with one public MAC address,thereby achieving the objective of the invention.

FIG. 3 is a flowchart of transmission of a downlink Layer 2 packetaccording to an embodiment of the invention. As shown in FIG. 3, thedetailed steps are described as follows:

Step 301: The convergence layer device sends a downstream packet to theaccess device.

If detecting that the upstream packet sent by the access device includesa special packet character information field, the convergence layerdevice determines that the upstream packet is a packet without thecharacter information thereof. The convergence layer device stores thecharacter information of the packet and adds the character informationinto the downstream packet when sending the corresponding downstreampacket. For example, the character information of the packet may beadded to the Immediate Relay Agent field of the downstream packet if thedownstream packet is a PPPoE packet.

Step 302: Upon receiving the downstream packet, the access deviceextracts the character information of the packet.

The packet character information extracted in this step is the same asthe packet character information adopted in the process of convertingthe MAC address of the upstream packet. For example, if the accessdevice uses the source IP address of the upstream packet as the packetcharacter information, the downstream packet character informationextracted by the access device in this step should be the destination IPaddress of the packet. If the access device uses the session ID of theupstream packet as the packet character information, the downstreampacket character information extracted by the access device in this stepshould also be the session ID of the packet. If the access device usesthe destination IP address of the upstream packet as the packetcharacter information, the downstream packet character informationextracted by the access device in this step should be the source IPaddress of the packet. If the access device uses the user portinformation of the upstream packet as the packet character information,the packet character information extracted by the access device in thisstep should also be the user port information of the packet, andmeanwhile, the field carrying the user port information should bedeleted from the downstream packet.

Step 303: According to the extracted packet character information, theaccess device finds the source MAC address corresponding to the packetcharacter information from the self-stored index relationship betweenthe packet character information and the source MAC address, that is,the MAC address of the user terminal to which the packet is sent.

Step 304: The access device replaces the destination MAC address of thepacket with the found source MAC address and sends the packet to theuser terminal corresponding to the source MAC address.

In a special case, if the downstream packet is an ARP request packet,the access device broadcasts the packet directly to the correspondinguser terminal after receiving the packet.

It can be seen that, by the process as shown in FIG. 3, the downstreampacket corresponding to the upstream packet of which the MAC address hasbeen converted is able to be sent to the user terminal accurately.

Based on the method provided in the invention, an access device is alsodisclosed.

FIG. 4 is the first schematic diagram illustrating the structure of anaccess device transmitting a Layer 2 packet according to an embodimentof the invention. As shown in FIG. 4, the access device includes an MACaddress conversion module 41 and a user terminal MAC address determiningmodule 42.

The MAC address conversion module 41 serves to store the correspondingrelationship between packet attribute information and public MACaddresses. Upon receiving an upstream packet sent by a user terminal,MAC address conversion module 41 finds the public MAC addresscorresponding to the packet according to the attribute information ofthe packet and the corresponding relationship thereof. Then MAC addressconversion module 41 replaces the source MAC address of the packet withthe public MAC address, sends the packet to the convergence layer deviceand then stores the index relationship between the packet characterinformation and the source MAC. On the other hand, upon receiving a userterminal MAC address request which carries the packet characterinformation from the user terminal MAC address determining module 42,the MAC address conversion module 41 returns the MAC address of the userterminal to the user terminal MAC address determining module 42.

The user terminal MAC address determining module 42 serves to extractthe character information of the packet after receiving the downstreampacket sent by the convergence layer device. The user terminal MACaddress determining module 42 makes the packet character informationcarried in the user terminal MAC address request and sends the packetcharacter information to the MAC address conversion module 41. Then, theuser terminal MAC address determining module 42 replaces the destinationMAC address with the user terminal MAC address returned by the MACaddress conversion module 41 and sends the packet to the correspondinguser terminal.

As an existing access device mainly includes a hardware processing unitand a software processing unit, wherein the hardware processing unitmainly serves to receive, analyze and forward a packet from the userside and the network side and meanwhile controls the extraction of thepacket attribute information and the transmission of the packet, the MACaddress conversion module 41 and the user terminal MAC addressdetermining module 42 provided in an embodiment of the invention are setin the hardware processing unit.

Furthermore, as shown in FIG. 5, the access device provided in anembodiment of the invention may includes an application layer MACaddress conversion module 43 and an application layer user terminal MACaddress determining module 44. The two modules are both located in thesoftware processing unit for the Layer 2 MAC address conversion of anapplication layer associated packet.

The application layer MAC address conversion module 43 is for use in,upon receiving an application layer associated upstream packet sent bythe hardware processing unit, sending a public MAC address request whichcarries the attribute information of the packet to the MAC addressconversion module 41, replacing the source MAC address of the packetwith the public MAC address returned by the MAC address conversionmodule 41, and then sending the packet to a forwarding module in thehardware processing unit of the access device. The forwarding modulesends the packet to the convergence layer device and sets up the indexrelationship between the character information of the packet and thesource MAC address of the packet. On the other hand, upon receiving theuser terminal MAC address request sent by the application layer userterminal MAC address determining module 44, the application layer MACaddress conversion module 43 regards the source MAC addresscorresponding to the packet character information as the MAC address ofthe user terminal and returns the source MAC address to the applicationlayer user terminal MAC address determining module 44.

The application layer user terminal MAC address determining module 44,upon receiving the application layer associated downstream packet sentby the hardware processing unit of the access device, sets the characterinformation of the packet in the user terminal MAC address request andsends it to the application layer MAC address conversion module 43, andreplaces the destination MAC address of the downstream packet with theuser terminal MAC address returned by the application layer MAC addressconversion module 43. Then the application layer user terminal MACaddress determining module 44 sends the packet to the forwarding modulein the hardware processing unit of the access device, which sends thedownstream packet to the corresponding user terminal.

Furthermore, as shown in FIG. 6, the application layer MAC addressconversion module 43 disclosed in the embodiment also includes a userport information obtaining module 431. The user port informationobtaining module 431 serves to receive the application-associatedupstream packet sent by the hardware processing unit and detects thepacket. If detecting that the packet contains no character information,the user port information obtaining module 431 acquires the user portinformation of the packet from the hardware processing unit and regardsthe user port information returned by the hardware processing unit asthe character information of the packet.

The foregoing description of the exemplary embodiments of the inventionhas been presented only for the purposes of illustration and descriptionand is not intended to be exhaustive or to limit the invention to theprecise forms disclosed. Many modifications and variations are possiblein light of the above teaching.

The embodiments were chosen and described in order to explain theprinciples of the invention and their practical application so as toactivate others skilled in the art to utilize the invention and variousembodiments and with various modifications as are suited to theparticular use contemplated. Alternative embodiments will becomeapparent to those skilled in the art to which the present inventionpertains without departing from its spirit and scope. Accordingly, thescope of the present invention is defined by the appended claims ratherthan the foregoing description and the exemplary embodiments describedtherein.

1. A method for Layer 2 packet transmission, comprising: receiving, byan access device, a packet from a user terminal; finding a correspondingpublic media access control (MAC) address from a correspondingrelationship between packet attribute information and a MAC addressaccording to attribute information of the packet, wherein thecorresponding relationship is configured in the access device; replacinga source MAC address in the packet with the public MAC address; andsending the packet with the public MAC address to a convergence layerdevice.
 2. The method according to claim 1, wherein the packet attributeinformation comprises the type of a protocol adopted by the packet, orthe type of link bearing the packet, or the type of a user group towhich the user terminal sending the packet belongs.
 3. The methodaccording to claim 1, further comprising: after the access device findsthe corresponding public MAC address, the access device obtainingcharacter information of the packet and setting up an index relationshipbetween the character information of the packet and the source MACaddress of the packet, wherein the character information is characterinformation of uniqueness distinguishing the packet from others.
 4. Themethod according to claim 3, wherein the character information of thepacket is obtained from the packet and comprises a source internetprotocol (IP) address, or a session identifier (ID), or a destination IPaddress of the packet.
 5. The method according to claim 4, furthercomprising: the access device receiving a packet from the convergencelayer device, extracting the packet character information from thepacket, finding the corresponding source MAC address from the indexrelationship according to the character information of the packet, andsending the packet to the user terminal.
 6. The method according toclaim 3, wherein the character information of the packet is user portinformation corresponding to the packet and the obtained characterinformation of the packet is carried into the packet.
 7. The methodaccording to claim 6, wherein the user port information comprises frameinformation, slot information and a port number of the access devicereceiving the packet, or the source MAC address of the packet, or theframe information, slot information and port number of the access devicereceiving the packet as well as the source MAC address of the packet. 8.The method according to claim 6, wherein the packet comprises a firstpacket supporting a point-to-point protocol over Ethernet (PPPoE), or aDynamic Host Configuration Protocol (DHCP) from the user terminal. 9.The method according to claim 8, wherein the obtained characterinformation of the packet is carried in an Immediate Relay Agent fieldwhen the packet is the first packet supporting the PPPoE from the userterminal.
 10. The method according to claim 6, further comprising: uponreceiving the packet from the access device, the convergence layerdevice storing the character information carried in the packet andsetting the character information in a downstream packet before sendingthe downstream packet to the access device; and upon receiving thedownstream packet, the access device extracting the characterinformation from the downstream packet, finding the source MAC addresscorresponding to the extracted character information according to theself-stored index relationship between the character information of thepacket and the source MAC address, replacing the destination MAC addresswith the source MAC address and sending the downstream packet to thecorresponding user terminal.
 11. An access device, comprising a mediaaccess control (MAC) address conversion module adapted for: receiving anupstream packet from a user terminal; finding a public MAC addresscorresponding to the upstream packet according to self-storedcorresponding relationship between packet attribute information and thepublic MAC address; replacing a source MAC address of the upstreampacket with the public MAC address; and sending the upstream packet withthe public MAC address to a convergence layer device.
 12. The accessdevice according to claim 11, wherein the MAC address conversion moduleis located in a hardware processing unit of the access device.
 13. Theaccess device according to claim 11, further comprising a user terminalMAC address determining module adapted for: receiving a downstreampacket from the convergence layer device; carrying character informationof the downstream packet in a user terminal MAC address request; sendingthe user terminal MAC address request to the user terminal MAC addressconversion module; replacing a destination MAC address of the downstreampacket with the user terminal MAC address returned by the user terminalMAC address conversion module; and sending the downstream packet to thecorresponding user terminal, wherein the user terminal MAC addressconversion module is further adapted for: use in storing an indexrelationship between the packet character information and the source MACaddress; finding the corresponding source MAC address in the indexrelationship upon receiving the user terminal MAC address requestcarrying the packet character information; and sending the source MACaddress as the user terminal MAC address to the user terminal MACaddress determining module; and wherein the character information ischaracter information of uniqueness distinguishing the packet fromothers.
 14. The access device according to claim 13, wherein the userterminal MAC address determining module is located in the hardwareprocessing unit of the access device.
 15. The access device according toclaim 11, further comprising an application layer MAC address conversionmodule located in a software processing unit of the access device, andadapted for: obtaining the public MAC address of the upstream packetfrom the MAC address conversion module upon receiving the applicationlayer associated upstream packet from the hardware processing unit ofthe access device; replacing the source MAC address of the upstreampacket with the obtained public MAC address; and sending the upstreampacket with the public MAC address to a forwarding module in thehardware processing unit of the access device.
 16. The access deviceaccording to claim 15, further comprising an application layer userterminal MAC address determining module located in the softwareprocessing unit of the access device, and adapted for: receiving theapplication layer associated downstream packet sent from the hardwareprocessing unit of the access device; requesting the corresponding userterminal MAC address from the application layer MAC address conversionmodule according to the character information of the packet; replacingthe destination MAC address of the downstream packet with the userterminal public MAC address returned from the application layer MACaddress conversion module; and sending the packet to the forwardingmodule in the hardware processing unit of the access device, wherein theapplication layer MAC address conversion module is further adapted for:storing the index relationship between the packet character informationand the source MAC address; and according to the request from theapplication layer user terminal MAC address determining module,returning the source MAC address corresponding to the packet characterinformation sent from the application layer user terminal MAC addressdetermining module as the application layer user terminal MAC address tothe user terminal MAC address determining module.
 17. The access deviceaccording to claim 15, wherein the application layer MAC addressconversion module further comprises a user port information obtainingmodule adapted for: receiving the upstream packet sent by the hardwareprocessing unit; acquiring the user port information of the packet fromthe hardware processing unit; and setting the acquired user portinformation as the character information of the packet.